ABSTRACT

The COVID-19 (COronaVIrus Disease) pandemic has been spreading globally and social isolation has been implemented as an effective solution to limit the spread of the pandemic before vaccines are developed successfully. The reduction of human activities during social isolation is leading to an improvement in air quality being observed worldwide. In this study, we analysed satellite TROPOMI (TROPOspheric Monitoring Instrument) NO₂ (Nitrogen Dioxide) and OMI (Ozone Monitoring Instrument) NO₂ products obtained from Sentinel-5P and Aura satellites, respectively, during the social isolation from 1 April 2020 to 22 April 2020 in Vietnam where air pollution is a serious environmental issue. Both TROPOMI and OMI NO₂ have shown low agreement with local on-ground NO₂ concentration (the correlation coefficient r equals 0.4 and 0.3 in 2020, respectively) but have had moderate correlation with each other in 2020 (r equals 0.81 for two annual averaged maps). In addition, the moderate available data ratio over cloudy northern areas were observed, especially for TROPOMI datasets. During social isolation, the national average NO₂ decreased by 9.3% for TROPOMI and 7.2% for OMI, respectively, in comparison with the same periods in the previous years. The reduction was stronger in the North than in the South and lasted for one more month after the lockdown period. The decrease of NO₂ density during the lockdown was observed strongly in urban areas associated with dense population, traffic density, and industrial zones. Further analysis of NO₂ density for Ho Chi Minh city revealed a decreasing trend of NO₂ during social isolation (16.62% and 11.77% compared with the previous month and the same period in 2019, respectively). Furthermore, we used a random forest model to estimate the NO₂ density (normal life situations) based on daily meteorological data at station. During social isolation, NO₂ density observed in Ho Chi Minh city decreased by 26% down to that of normal life situations. The NO₂ reduction has shown strong anthropogenic impact on air pollution over the study area. Besides, the first use of TROPOMI and OMI NO₂ products together has highlighted potentials of satellite observation for air quality monitoring and analysis in Vietnam where on-ground measurements are very limited.

摘要

COVID-19（冠状病毒病）大流行已在全球蔓延，社会隔离已作为有效解决方案，在疫苗研制成功之前限制大流行的传播。社会隔离期间人类活动的减少正在导致全球空气质量的改善。在这项研究中，我们分析了2020 年 4 月 1 日至 22 日社会隔离期间从 Sentinel-5P 和 Aura 卫星获得的卫星 TROPOMI（对流层监测仪器）NO ₂（二氧化氮）和 OMI（臭氧监测仪器）NO ₂产品2020 年 4 月在越南，空气污染是一个严重的环境问题。TROPOMI 和 OMI NO ₂与当地地面 NO 的一致性较低₂浓度（相关系数r在 2020 年分别等于 0.4 和 0.3），但在 2020 年彼此之间具有中等相关性（两个年平均图的r等于 0.81）。此外，观察到北部多云地区的中等可用数据比率，尤其是 TROPOMI 数据集。在社会隔离期间，与往年同期相比，TROPOMI 和 OMI的全国平均 NO _{2 分别}下降了 9.3% 和 7.2%。北方的减少幅度大于南方，并且在封锁期后又持续了一个月。NO ₂的减少在与人口稠密、交通密度和工业区相关的城市地区，人们强烈地观察到封锁期间的人口密度。NO的进一步分析₂密度胡志明市没有透露的下降趋势₂社会隔离期间（16.62％和11.77％，与上月和2019年同期相比分别）。此外，我们使用随机森林模型来估计基于站日常气象数据的 NO ₂密度（正常生活情况）。在社会隔离期间，胡志明市观察到的NO ₂浓度下降了 26%，降至正常生活情况下的水平。NO ₂减少已显示出对研究区域空气污染的强烈人为影响。此外，TROPOMI 和 OMI NO ₂产品的首次使用凸显了卫星观测在越南进行空气质量监测和分析的潜力，因为越南的地面测量非常有限。